基于比较器LM393的频率计，通过单片机定时器可以测出频率值。-LM393 comparator-based frequency counter, through the microcontroller timer frequency can be measured.

可燃气体报警器QM-N5，所出的声音较小，可以试着把100UF电容调到2200UF。面包板上做过实验，可行。比较器用了LM393。-Combustible gas alarm, the sound is small, you can try capacitance transferred 2200UF.